The present invention relates to forestry grapples and more specifically relates to pivot joint structures for suspending grapples from support booms.
It is known to suspend grapples from support booms by means of pivot joint structures which permit the grapple to swing about separate horizontal axes located crosswise to each other. One problem with such suspensions is that when the vehicle carrying the grapple is operated over rough terrain while the grapple is empty the grapple flops wildly about these axes and sometimes comes into contact with the support boom or other vehicle structure which may result in damage to the grapple, boom and/or other structure.
To overcome the problem of grapple flop, it is known in the prior art to provide grapple pivot structures with various types of friction brakes which inhibit such flop. These friction brakes suffer from one or more of the drawbacks of requiring frequent adjustment, of requiring the joint structure to be disassembled for servicing brake parts, of lacking flexibility for modifications for changing braking capacity, and of having the braking surfaces arranged such that dirt, lubricants and other foreign substances come into contact therewith and diminish the life and/or effectiveness thereof.